The present invention relates to a coating apparatus. More particularly, the present invention relates to an improvement in a coating apparatus of the type comprising a coating vessel rotatably supported at one end and connected to a vacuum source by a coaxially arranged and co-rotatable tube having a spray nozzle disposed at one end of a liquid conduit and a discharge opening closable by a cover arranged at an unsupported end of the discharge vessel.
A known coating apparatus of the above-mentioned type is disclosed in German DE-PS No. 2,319,960. A tube rotatable together with the coating vessel comprises a hollow shaft with the coating vessel being fixed at one end of the shaft. The hollow shaft extends through a bearing disposed directly adjacent the coating vessel and is connected with a drive unit at a side of the bearing remote from the coating vessel. The discharge opening is located axially opposite the hollow shaft and is closed by a cover which is carried exclusively by the coating vessel. It is customary for such covers to be connected with the coating vessel by hinges so as to be pivotable away from the coating vessel and, when in closed position, to be held in abutment against an edge of the discharge opening by a clamping device. A liquid conduit extends through the hollow shaft.
The discharge opening of this known coating apparatus is readily accessible since the coating vessel is supported at only the end remote from the discharge opening. However, the portion of the coating vessel which is adjacent the hollow shaft and the hollow shaft itself are not readily accessible for cleaning. This arrangement presents a disadvantage because, during coating, a generally sticky coating substance is sprayed into the coating vessel by the spray nozzle while the coating vessel is connected to a vacuum source through the hollow shaft. This arrangement provides the material to be coated, while being exposed to the spraying, with the best possible venting so that the material fully accepts the coating substance. With this procedure however, droplets of the coating substance suspended in the coating vessel, perhaps combined with dust particles of the material to be coated, are drawn by the vacuum into the area of the coating vessel which is connected to the hollow shaft and thus into the hollow shaft itself where the droplets of the coating substance form a firmly adhering coating on the hollow shaft.
Therefore, it is an object of the present invention to provide a coating apparatus of the above-described type which permits easier cleaning of both the coating vessel and the tube that is rotated together with the coating vessel.
This object and others are achieved in accordance with the present invention, by arranging the cover on the rotatable tube. In addition, the rotatable tube is supported separately from the coating vessel and guided for movement along the axis of rotation of the coating vessel.
In this way, the entire inner wall of the coating vessel, including the area remote from the cover for the discharge opening, may be smooth and is readily accessible through the discharge opening. Also, the tube which is rotatable together with the coating vessel and, in operation, connects the coating vessel with the vacuum source, is more accessible when the cover is removed than in the known coating apparatus. The reason for the improved accessibility is that the rotatable tube is arranged to move away from the coating vessel together with the cover so that the end of the rotatable tube which faces the coating vessel during operation is accessible directly rather than through only the coating vessel as in the known coating apparatus.
In a preferred embodiment of the present invention the rotatable tube is guided for axial movement by telescopic displacement within a rotatable piece of pipe which is supported by and sealed in a bearing box arranged to pivot away from the coating vessel. The distance over which the rotatable tube is axially displacable need only be sufficient so that the cover can be detached from the coating vessel without immediately affording full access to the discharge opening. The accessibility of the discharge opening as well as the inside of the cover is attained when the bearing box is pivoted away from the coating vessel together with the rotatable tube, the piece of pipe, and the cover.
The rotatable tube and the piece of pipe can be sealed directly with respect to each other by arranging one inside the other with a small clearance. However, it is preferred to provide sufficient radial clearance between the two so that any clamping or bending loads can be prevented in case the cover should take a somewhat eccentric position with respect to the axis of rotation when the coating vessel is closed. Therefore, in the preferred embodiment of the present invention the tube and the piece of pipe are tightly connected by a bellows. The bellows readily balances any axial misalignment between the tube and the piece of pipe.
Preferably, the bearing box is supported on a strut arranged for pivotal movement about a first pivot axis which intersects the axis of rotation of the coating vessel. The strut is pivotable about a second pivot axis which is spaced from and parallel to the first pivot axis. This arrangement can be produced at low cost and affords a particularly simple handling of the cover.
When the liquid conduit comprises a jet tube extending through the rotatable tube into the coating vessel, as is the case in the known coating apparatus described above, the jet tube of the coating apparatus according to the present invention preferably is fixed to the bearing box which is adapted to be swung away from the coating vessel. With this arrangement, the nozzle is also readily accessible for cleaning and replacement once the cover has been removed from the coating vessel.